linux-kernel - Re: [PATCH 4/4] capture pages freed during direct reclaim for allocation by the reclaimer

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Date:	Wed, 01 Oct 2008 10:01:46 -0500
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Andy Whitcroft <apw@...dowen.org>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 4/4] capture pages freed during direct reclaim for allocation
 by the reclaimer

Andy Whitcroft wrote:
> When a process enters direct reclaim it will expend effort identifying
> and releasing pages in the hope of obtaining a page.  However as these
> pages are released asynchronously there is every possibility that the
> pages will have been consumed by other allocators before the reclaimer
> gets a look in.  This is particularly problematic where the reclaimer is
> attempting to allocate a higher order page.  It is highly likely that
> a parallel allocation will consume lower order constituent pages as we
> release them preventing them coelescing into the higher order page the
> reclaimer desires.

The reclaim problem is due to the pcp queueing right? Could we disable pcp
queueing during reclaim? pcp processing is not necessarily a gain, so
temporarily disabling it should not be a problem.

At the beginning of reclaim just flush all pcp pages and then do not allow pcp
refills again until reclaim is finished?
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